1. Field of the Invention
The present invention relates to an X-ray mask support for use in X-ray lithography, an X-ray mask structure using tills X-ray mask support, and an X-ray exposure method using of the X-ray mask structure.
2. Related Background Art
Heretofore, much attention has been paid to X-ray lithography as a promising technique for the formation of an extremely fine pattern having a minimum line width of 1 .mu.m or less, for example, the formation of a fine pattern for semiconductor devices. With the reduction of the line width of the pattern on integrated circuits which is required to satisfy density increase and speed-up of semiconductor integrated circuits in recent years, various techniques particularly regarding an X-ray mask support and an X-ray mask structure have been investigated to improve the resolution of the fine pattern of an X-ray absorber which is formed on the X-ray mask structure. The X-ray mask support for use in the X-ray lithography is mainly comprised of an X-ray permeable film and a support frame for supporting the X-ray permeable film. Furthermore, the X-ray mask support having a desired X-ray absorber fine pattern on the X-ray permeable film is called the X-ray mask structure.
As some improved examples of conventional techniques, for example, Japanese Patent Publication No. 53-24785 describes an example using a silicon carbide film as the X-ray permeable film obtained by a CVD method. In addition, Japanese Patent Publication No. 54-27711 describes the X-ray mask structure which can be obtained by forming a silicon nitride layer having a thickness of 0.5 .mu.m or less as to be adjacent to the support frame by a conventional manner such as the CVD method, and then forming a silicon carbide layer having a thickness of 5 .mu.m or less on the silicon nitride layer by the use of a gas containing C and H such as methane, ethylene or acetylene in accordance with a plasma reaction to produce a two-layer composite film as the X-ray permeable film. In this kind of X-ray mask structure, mechanical strength and productivity which are conventional problems to be solved can be mainly improved. Moreover, since this composite film is provided with the silicon nitride layer which is adjacent to the support frame, the X-ray permeable film also has excellent resistance to an alkali at the time of the formation of the support frame.
However, in the above-mentioned conventional X-ray mask structures, if the X-ray permeable film is constituted of a single layer film, X-ray permeability and visible/near infrared ray permeability of alignment light are not considered to be sufficient, which causes the deterioration of throughput and alignment precision.
Furthermore, in the case that the X-ray permeable film comprises a multi-layer structure film of silicon carbide and silicon nitride, the X-ray mask structure bends and strain occurs therein inconveniently owing to a difference of thermal expansion coefficients inherent in the materials constituting the respective layers, when heated by the irradiation of X-rays. This drawback leads to the deterioration of mask precision, and so the above-mentioned film structure is unsuitable as the X-ray mask support in which extremely strict position precision is required. Moreover, when the multi-layer composite film comprising such different kinds of materials is employed as the X-ray permeable film, manufacturing devices and manufacturing processes are complicated. Particularly, when the CVD method utilized, a specific gas such as a silane gas must be used, so that hazard increases and a large facility investment for the safety assurance is required, which is not economical.